As the time evolves to the 21st century, the network economy driven by Internet has been submerged in excessive bubbles, under which the Internet falters and is facing a variety of challenges ahead, including the compromise between cost and demand, Quality of Service and technical difficulties, transition to the next generation Internet Protocol Version 6 (IPv6), seeking for new value chains and profitability models, and challenges in network, information security, etc. Next Generation Networks (NGN) require support from many new techniques, in which the foreseeable techniques include IPv6 technique, high speed optical fiber transmission technique, optical switching and intelligent optical network technique, broadband access technique, metropolitan area network (MAN) technique, soft switch technique, the third generation (3G) and post 3G mobile communication techniques, network security technique, etc. Among these techniques, the soft switch technique is one of the key techniques supporting NGN.
Soft switch technique is designed to completely separate control function (including service control function and network resource control function) from transmission function. NGN is required to utilize the soft switch technique. The concept of soft switch is based on the new layered model of network functions including access and transport layer, media layer, control layer, and network service layer, and is employed to integrate/separate the functions in different degrees and enable the service providers to combine service transmission and control protocols flexibly through a variety of interface protocols, so as to implement service integration and transition. Therefore, the soft switch technique is very suitable for coexistence and intercommunication of different networks and is also applicable to evolution from voice-based network to multi-service multimedia network. The interface protocol H.248/MEGACO between Media Gateway Controller (MGC) and Media Gateway (MGW) approved jointly by International Telecommunication Union (ITU) and Internet Engineering Task Force (IETF) is a key protocol and reflects the great efforts for promotion of NGN in the telecommunication field and the Internet field.
Soft switch technique requires to separate call control function from MGW, i.e., from the transport layer, and to implement with software the connection control, translation and route selection, gateway management, call control, bandwidth management, signaling, security, call detail record generation, etc. This separates control from service provision. Soft switch in a packet switched network provides the same function as circuit switched network. Accordingly, a soft switch is also referred to as a call proxy or a call server. Soft switch technique is service-independent and is a technique that provides telecommunication services over Internet Protocol (IP) networks. In a circuit switched network, call control, service provision, and switching matrix are integrated in one system. In contrast, the essence of soft switch lies in the separation of service and control from transmission and access, so that the entities may connect with each other and communicate with each other using standard protocols, so as to provide services in a more flexible manner. In other words, a soft switch is a software-based distributed switching/control platform, which separates call control function from the media gateway, thereby facilitates the introduction of a variety of services into the network.
The soft switch is a function entity that provides call control and connection control functions for services with real-time requirement in NGN, and is the core for call and control in NGN. As an open entity, the soft switch has to employ open protocols for the external interfaces. The interface between MGW and soft switch is designed to support the soft switch to perform bearer control, resource control and management for the MGW, and this interface is the H.248 or MEGACO protocol. The interface between signaling gateway and soft switch is designed to transmit messages between the soft switch and the signaling gateway, and can employ the Signaling Control Transfer Protocol (SCTP) or other similar protocols. The interface between soft switches is designed to enable the interaction between the soft switches and can employ the Session Initial Protocol (SIP). The interface between soft switch and application/service layer is designed to provide access to a variety of databases, third-party application platforms, and function servers, so as to enable the support for various value added services, administrative services, and third-party applications.
After the separation of control and bearing, the H.248 protocol is used for transmission between MGC and MGW, so as to enable the control for MGW by MGC. In the MGW, there are generally multiple H.248 protocol processing modules, so as to meet the requirement for high traffic throughput. MGC can choose different links to transmit H.248 messages, so as to distribute the load between the individual H.248 processing modules. Different distribution modes have to be implemented in different mechanisms, such as primary/standby mode or load sharing mode. In the primary/standby mode, MGW chooses a primary link to transmit H.248 signaling messages, and chooses a standby link for transmission only when the primary link fails. In the load sharing mode, MGW chooses multiple links to share the load and transmit the H.248 signaling messages.
The major configuration information of an H.248 link includes: link number LinkNo which identifies the H.248 signaling link configured by the user; H.248 module identification ModuleID which identifies the module that processes the H.248 messages; local IP address LocalIPAddr which is the IP address configured for the local H.248 protocol processing module; local port number LocalPort which is the port number configured in the local H.248 protocol processing module; remote IP address RemoteIPAddr which is the IP address configured for the remote H.248 protocol processing module; and remote port number RemotePort which is the port number configured in the remote H.248 protocol processing module.
Message Transfer Part at level 3 Broadband (MTP3B) is a message transport protocol based on Asynchronous Transfer Mode (ATM), and is adapted to transmit messages between signaling points in the signaling network. MTP3B employs Signaling Point Codes (SPCs) to identify the nodes in the signaling network, and transmits messages through the MTP3B links established between these nodes. Multiple MTP3B links can be established between a pair of signaling points, and each link is identified with a unique Signaling Link Code (SLC). MTP3B chooses an appropriate signaling route and link having the highest priority level currently in the route list configured in the present signaling point in accordance with the routing information contained in the Route Label in the signaling message, so as to send the user's message to the specified destination signaling point properly via the signaling route and link. The routing information in the Route Label mainly includes:
Network Identification (NI), which identifies the network type of the signaling point; the value of NI can be “International”, “International Standby”, “Domestic”, “Domestic Standby”, etc.
Original Point Code (OPC), which indicates the code value of the original signaling point, and may uniquely identify, together with NI, a signaling point that is the starting point for message transmission. The value range of OPC depends on the type of the signaling point code: if the type of the signaling point code is of 14-bit type, the value of OPC is 0˜0x3fff; if the type of the signaling point code is of 24-bit type, the value is 0˜0xffffff;
Destination Point Code (DPC), which indicates the code value of the destination signaling point, and can uniquely identify, together with NI, a destination signaling point that is the destination for message transmission; DPC has the same value range as OPC; Signaling Link Selection (SLS), in 4 bits, which is used by MTP3B to enable load sharing between multiple MTP3B links.
MTP3B can transmit a variety of messages, such as H.248 messages and Radio Access Network Application Part (RANAP) messages. The message transmission in MTP3B has many advantages over other message transmission methods (e.g., message transmission over IP link). For example, the MTP3B transport layer is ATM layer, while the ATM transmission technique incorporates advantages of both of circuit switched and packet switched, so ATM can not only provide reliable QoS guarantee but also support service transmission at diverse data rates, thereby can meet the requirement for the development of broadband. In addition, by utilizing the ATM transmission technique, it is enabled to take full advantage of the existing E1/T1 resources, provide more flexible networking modes and reduce the cost of network transmission.
In many existing networks, message transmission between MGC and MGW is generally via IP links. A typical networking mode in 3G is shown in FIG. 1 which shows the networking between the access systems (including 3G mobile station, base station, Radio Network Controller (RNC)) and MGW and MGC. The RNC is connected to MGW over ATM. The transmission of H.248 messages between MGC and MGW is based on IP. The protocol stack for transmission is H.248/SCTP/IP. In MGW, multiple H.248 protocol processing modules are used to meet the requirement for high traffic throughput. Each of those modules provides an Ethernet interface to connect with MGC. Through the H.248 links configured between those modules, H.248 messages can be transmitted over IP between MGC and MGW.
In the practical applications of the above described solution, only Ethernet resources can be used during the transmission of H.248 messages between MGW and MGC over IP. This results in a limited networking flexibility. The operator will have to update many legacy network resources, which brings about a high cost in network construction.
This problem is resulted from the fact that the transmission of H.248 messages between existing MGC and MGW is via IP links, which can not take the advantages of ATM network resources and networking.